multilock is a Go library allowing to store multiple sync.Mutex or sync.RWMutex.

The main benefit is to reduce the memory footprint if we need to have a mutex for every single structure of a set (e.g. thousand of maps or slices).

The internal data structure managed by multilock, depending on the use case, has either a fixed or a variable length.

• Fixed length structure of Mutex: multilock.Fixed
• Fixed length structure of RWMutex: multilock.RWFixed
• Variable length structure of Mutex: multilock.Var
• Variable length structure of RWMutex: multilock.RWVar

In the following example, we will create a 1/10 ratio multilock (10 mutexes to handle 100 maps):

const multilockLength = 10
const customStructLength = 100

// Initialize a fixed length multilock structure
mlock := multilock.NewFixed(multilockLength)

// Create custom structures
maps := make([]map[string]string, customStructLength)
for i := 0; i < customStructLength; i++ {
	maps[i] = make(map[string]string)
}

// Retrieve a lock for a given maps index
mutex := mlock.Get(maps[42])
mutex.Lock()
defer mutex.Unlock()

Internally, multilock has a distribution strategy which is basically hashing the key and returning a modulo based on the length provided.

It is also possible to override this distribution strategy this way:

mlock := multilock.NewFixed(10, multilock.WithCustomDistribution(func(i interface{}, length int) int {
    // Return an int between 0 and 10 depending on our distribution strategy
}))

The last point is related to variable length structures. In this example, we will create one and resize it:

mlock := multilock.NewVar(10)
mlock.Resize(15)

The resize operation is safe. To access/resize a variable length structure, it requires to acquire a shared lock first (which does not exist for a fixed structure hence making it faster than a variable one).